One in 4 persons in the U.S. stop, skip, or do not start a medication because of cost, and the 24 million U.S. residents with diabetes are especially vulnerable. Such cost-related medication nonadherence worsens disease control, and increases risk for emergency department visits, hospitalizations, and mortality. Study. We propose to collaborate with Hawaii's BlueCross BlueShield (BCBS) to examine if our ongoing, highly successful hardcopy/web-based Prescribing Guide (PG) www.PrescribingGuide.com improves medication adherence and lowers drug costs for persons with diabetes by helping physicians easily know drug costs when prescribing. The PG summarizes multiple formularies in a standard format, highlights widely covered drugs, gives retail prices from discount pharmacies, and has links to assistance programs. In a statewide physician survey, 9 in 10 physicians said difficulty knowing drug costs prevented them from helping patients with medication costs. The PG achieved a 58% baseline uptake and 79% one-year retention. The website receives 4,100+ hits monthly. The PG is currently used by 194 community physicians and would cost less than $30,000/year to implement statewide (~2500 physicians). Written physician surveys indicate that it has doubled the percentage of physicians who said they checked formularies (67% vs. 34%) and often knew drug costs (29% vs. 11%). However, whether it would improve medication adherence and lower out-of-pocket drug costs is unknown. Our aims are: AIM 1: To determine if the Prescribing Guide improves medication adherence in persons with diabetes. AIM 2: To calculate whether the Prescribing Guide lowers out-of-pocket drug costs for persons with diabetes. Our strength is that BCBS insures 60% of the Hawaii's residents, making this a large population study. We will use BCBS claims to compare changes in medication adherence and drug costs (from 2007 to 2009) for patients whose physicians use the PG vs. patients whose physicians do not use the PG. Although not a RCT, this "difference of differences" approach will help to minimize bias. Innovation. The PG takes advantage of the internet (40% to 96%) being more widely used by physicians than more complex technology such as PDA (26% to 57%) or e-prescribing (10% to19%). Past interventions using PDA or e-prescribing software to give physicians drug costs information have generally had low uptake rates in community physicians (<20%) even when offered for free. In contrast, our high uptake and retention rates indicate that physicians find that the Prescribing Guide is easy to use and time-saving. Policy and Health. The PG is practical, popular with Hawaii's physicians, and if shown to improve medication adherence, could be easily translated nationwide by compiling formularies from the top 8-10 plans in each state/county, giving local retail prices, and by keeping links to national assistance programs. PUBLIC HEALTH RELEVANCE: This proposal aims to reduce rates of cost-related nonadherence (stopping, skipping, not starting medications due to cost) in persons with diabetes. We will collaborate with a major health in our state to examine if our ongoing, popular Prescribing Guide intervention to give drug cost information to 194 community physicians has improved medication adherence and lower out-of-pocket drug costs for their patients. If shown to be successful, the Prescribing Guide is practical and low-cost, and could easily be translated to other states, giving it tremendous potential to improve health nationwide.